The state news agency, Sana, cited a police source as saying that 45 people were killed and many others, most of them women and children, were injured in Jableh.

It reported that two bombs exploded at the main entrance of the town's bus station.

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Near-simultaneous car and suicide bombings hit the main bus station in Tartous

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Jableh's bus station was also targeted, along with the town's hospital

A suicide bomber also blew himself up at the entrance of the emergency department at Jableh National Hospital, it added.

A doctor at the hospital said it was bombed less than a minute after the bus station.

"Everything went into emergency mode, wounded people began arriving," Younes Hassan told the Reuters news agency.

The fourth blast reportedly occurred near the offices of Jableh's electricity directorate, on the outskirts of the Amara residential district.

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A media outlet linked to IS said the jihadist group had claimed responsibility for the attacks

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Russia said the attacks underlined the fragile situation in Syria

In Tartous, more than 33 people were killed and 47 injured, Sana said.

A car bomb was detonated at the main gate to the city's bus station, while a suicide bomber detonated an explosive vest inside the facility, it added.

Bus driver Nizar Hamade told Reuters that the blasts occurred no more than 10 seconds apart.

"People began running but didn't know which direction to go, cars were on fire, there was blood and bodies on the ground," he added.

Another suicide bomber blew himself up in a western residential area of Tartous, Sana reported.

The Syrian Observatory for Human Rights, a UK-based monitoring group which relies on a network of sources on the ground, reported that 97 people were killed in Jableh and another 48 in Tartous.

It also said the two bombings at the bus station in Jableh were suicide attacks.

Information Minister Omran al-Zoubi said terrorist groups were resorting to bomb attacks against civilians because they were unable to fight the Syrian army.

"We will not be deterred," he told al-Ikhbariya TV. "We will use everything we have to fight the terrorists."

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Russia, which has an airbase near Jableh, said it was ready to combat "the terrorist threat"

Russia expressed concern at the blasts and said they underscored the need to revive the UN-led peace talks between the government and opposition, which broke down last month amid mounting violence.

"Of course a rise in tension and terrorist activity cannot but heighten concern. It is further proof of how fragile the situation is in Syria and demonstrates the necessity to continue active steps towards resuming talks," Kremlin spokesman Dmitry Peskov told reporters in Moscow.

President Vladimir Putin later sent his condolences to Mr Assad and reiterated his readiness to help the Syrian government combat "the terrorist threat".

IS, which controls large parts of northern and eastern Syria, carried out suicide bombings in the capital Damascus and the western city of Homs earlier this year.